Method for forming fine structure

ABSTRACT

In order to form three or more steps on a substrate with high precision, a first mask is formed to an area on the substrate corresponding with every other step, and also etching is performed on the area of the substrate to which the first mask is not formed, a second mask is formed to an area on the substrate to which the first mask has not been formed, and also etching is performed on the area on the substrate to which the first and the second masks are not formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing finestructures such as diffraction grating and the like.

2. Description of Related Art

Known binary optics manufacturing methods wherein a resist is formedinto a step-like formation by means of electron beam exposure anddeveloping, and using the structure as a diffraction pattern(diffraction grating), is disclosed in the Electronic CommunicationsJournal (c) J66-CP85-91 January 1983, Japanese Patent Laid-Open No.62-256601, Japanese Patent Laid-Open No. 62-42102, and so forth.

Also, Japanese Patent Laid-Open No. 61-137101 discloses art wherein twoor more types of films with etching endurance are layered to a certainthickness, and sequentially etched from the upper layer so as to form astair-like formation, which is made to serve as a mold for diffractionoptical devices. Also, Japanese Patent Laid-Open No. 61-44628 andJapanese Patent Laid-Open No. 6-160610 disclose art wherein resist isformed on a substrate one step at a time as an etching mask to form astair-like formation, which is made to serve as a mold for diffractionoptical devices.

Further, Japanese Patent Laid-Open No. 8-15510 discloses art wherein oneeach of a etching stopper layer and a transparent layer are layered on asubstrate, so as to directly form a stair-like formation, by means ofalignment, exposure, and etching, which is made to serve as adiffraction optical device.

Also, Japanese Patent Application 6-26339 and U.S. Pat. No. 5,324,600disclose art wherein alignment is performed each time the resist ispatterned, thus forming a stair-like structure of resist directly in thesubstrate as an etching mask, which is made to serve as a diffractionoptical device. Japanese Patent Laid-Open No. 7-72319, which correspondsto Application No. 6-26339, discloses art for forming a stair-likestructure by performing alignment with the resist as an etching mask.

FIG. 26 is a cross-sectional diagram illustrating the manufacturingprocess of a diffraction optical device of an 8-stepped structure. InStep (1) of FIG. 26, resist is dropped onto a cleansed substrate 1, andthe resist is formed into a thin film of 1 μm in thickness by means ofspin-coating, which is then baked to form the resist film 2. In Step (2)of FIG. 26, the substrate 1 is mounted to an exposure device capable ofexposing the finest diffraction grating pattern into the resist film 2,and exposure light L with sensitivity to the resist film 2 is castthereupon with a reticle 3 formed with a pattern according to thedesired diffraction grating pattern serving as a mask, therebyperforming exposure. In the event that a positive-type resist is used,the area exposed by the exposure light L becomes soluble to thedeveloping agent, and so a resist pattern 4 with the certain dimensionsis formed, as shown in Step (3) of FIG. 26. In Step (4) of FIG. 26, thesubstrate 1 is mounted to a responsive ion etching device or an ion beametching device capable of anisotropic etching, and the etching isperformed to the substrate 1 for a certain time to a certain depth, withthe patterned resist 4 as the etching mask. Then, removing the resistpattern (4) yields the substrate 1 formed with a pattern 5 having atwo-stepped stair-like pattern, as shown in Step (5) of FIG. 26.

Again, in Step (6) of FIG. 26, a resist film 6 is formed on thesubstrate 1 as with Step (1) and mounted on the exposing device, andfollowing alignment with alignment precision that the exposing devicehas to the pattern so far formed, with the reticle 7 having a two-foldcycle pattern of the diffraction pattern, following which the resistfilm 6 is exposed and developed to form an alignment pattern 8 in Step(7) of FIG. 26. Next, removing the resist pattern following dry etchingas with Step (4) yields a four-stepped stair-like pattern 9, as shown inStep (8) of FIG. 26.

Further, in Step (9) of FIG. 26, a resist film 10 is formed on thesubstrate 1 as with Step (1), and with the reticle 11 having a four-foldcycle pattern of the diffraction pattern serving as the mask, a resistpattern 12 is formed in Step (10) of FIG. 26, in the same manner as withStep (7). Next, removing the resist pattern 12 following dry etchingyields a diffraction optical device with an eight-stepped stair-likepattern 13, as shown in Step (11) of FIG. 26.

Thus, diffraction optical devices or molds having a stair-likecross-sectional diagram, referred to as “binary optics”, can bemanufactured by exposure, lithography process based on etchingtechnique, and film-forming technique, these being used in semiconductormanufacturing art. The optical capabilities of such diffraction opticaldevices are exhibited based on the recessed and projected stair-likeform which is formed on the substrate, so the diffraction efficiencythereof is affected by the form, i.e., the depth, width, andcross-sectional form of the formed steps.

In the case of sequentially using such double-fold masks to form adiffraction optical device with a plurality of steps, an ideal 8-stepformation A can be manufactured using three masks 17 a through 17 c, asshown in FIG. 27, so long as there are no alignment errors ordimensional errors.

However, with the above example, in manufacturing technique using aplurality of masks, margin of error in the form of the steps owing tomargin of error in alignment markedly deteriorates diffractionefficiency, and once such an error in form is created it cannot berestored, which consequently raises costs. In reality, it is impossibleto completely do away with all such alignment margin of error anddimensional margin of error, so in the event that there is offset in thealignment of the masks 17 a through 17 c shown in FIG. 28 to the degreeof r1 and r2, a diffraction optical device is formed in the form of Binstead of the intended form A. Accordingly, the optical capabilitiessuch as diffraction efficiency greatly deteriorate, and in addition, inthe event that dimensional errors occur in each layer, the deteriorationof optical capabilities decreases even further.

For example, in the event that quartz is used as the substrate and anideal 8-stepped form as shown by form A is formed with a minimum linewidth of 0.35 μm, step height d of each of 61 nm, and usage wavelengthof 248 nm, the logical diffraction efficiency obtained by subtractingloss from reflection is 95%. On the other hand, in the event that themargin of error r1 between reticle 17 a and reticle 17 b is 80 nm, forexample, and the margin of error r2 between reticule 17 a and reticule17 c is 30 nm, the diffraction efficiency drops by 15% to 80% evenwithout taking reflection into consideration, and these results havebeen confirmed in actual measurement and simulation.

Also, in order to form a multi-stepped diffraction optical device with asimilar method, resist processing following a plurality of times ofexposing and developing is carried out, and a 16-stepped stair-likediffraction optical device can be manufactured using quartz as thesubstrate, with, e.g., a minimum line width of 0.35 μm, step height d ofeach of 30.5 nm, and usage wavelength of 248 nm. In the case of an ideal16-stepped form, the logical diffraction efficiency obtained bysubtracting loss from reflection is 99%, but in the event that margin oferror of alignment is included in this, the diffraction efficiency dropsfar below that of the 8-stepped form.

Thus, control of the dimensions and alignment of resist pattern is inactual practice is quite difficult, reproducibility cannot be obtained,and consequently, the steps become narrower or wider than intended, sothat grooves and protrusions non-existent in the ideal step formationare formed, and is problematic in that the optical capabilities of thediffraction optical device markedly deteriorate.

Also, while electron beam drawing does away with a margin of error inalignment, the immense amount of drawing creates a problem ofinefficient manufacturing through-put.

Further, generally, in the case of using glass for the diffractionoptical device, there is the need to form the resist thickly in order toobtain diffraction patterns with deep steps, since the etching speed isslow and the speed of etching the resist and the glass is approximatelythe same, and consequently, substances generated by reaction in etchingat the deep portions of the grove cannot find a way out in the eventthat the resist is thick, having an ill effect on the cross-sectionalform and disrupting the rectangular form of the side walls.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a forming methodwhereby fine steps can be formed at high precision.

The present invention is a method for forming three or more steps on asubstrate, the method comprising the steps of: forming a first mask toan area A1 on the substrate corresponding with every one other step, andalso performing etching and/or deposition to the area A2 on thesubstrate to which the first mask is not formed; and forming a secondmask to an area on the substrate to which the first mask has not beenformed, and also performing etching and/or deposition to the area on thesubstrate to which the first and the second masks are not formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a manufacturing process accordingto a first embodiment;

FIG. 2 is a cross-sectional diagram of a manufacturing process accordingto a second embodiment;

FIG. 3 is a cross-sectional diagram of a manufacturing process accordingto a third embodiment;

FIG. 4 is a cross-sectional diagram of a reflection-type diffractionoptical device according to a fourth embodiment;

FIG. 5 is a cross-sectional diagram of a diffraction optical deviceaccording to a fifth embodiment;

FIG. 6 is a configuration diagram of a projecting optical system;

FIG. 7 is a configuration diagram of a projecting exposing device;

FIG. 8 is a cross-sectional diagram of a manufacturing process accordingto a sixth embodiment;

FIG. 9 is a cross-sectional diagram of a manufacturing process accordingto the sixth embodiment;

FIG. 10 is a cross-sectional diagram of a manufacturing processaccording to a seventh embodiment;

FIG. 11 is a cross-sectional diagram of a manufacturing processaccording to the seventh embodiment;

FIG. 12 is a cross-sectional diagram of a manufacturing processaccording to an eighth embodiment;

FIG. 13 is a cross-sectional diagram of a manufacturing processaccording to the eighth embodiment;

FIG. 14 is a cross-sectional diagram of a manufacturing processaccording to a ninth embodiment;

FIG. 15 is a cross-sectional diagram of a manufacturing processaccording to the ninth embodiment;

FIG. 16 is a cross-sectional diagram of a reflection-type diffractionoptical device according to a tenth embodiment;

FIG. 17 is a cross-sectional diagram of a manufacturing processaccording to an eleventh embodiment;

FIG. 18 is a cross-sectional diagram of a manufacturing processaccording to the eleventh embodiment;

FIG. 19 is a cross-sectional diagram of a manufacturing processaccording to the eleventh embodiment;

FIG. 20 is a cross-sectional diagram of a manufacturing processaccording to an twelfth embodiment;

FIG. 21 is a cross-sectional diagram of a manufacturing processaccording to the twelfth embodiment;

FIG. 22 is a cross-sectional diagram of a manufacturing processaccording to an thirteenth embodiment;

FIG. 23 is a configuration diagram of a stepper according to afourteenth embodiment;

FIG. 24 is a perspective diagram of a stair-formed diffraction opticaldevice;

FIG. 25 is a cross-sectional diagram of a stair-formed diffractionoptical device;

FIG. 26 is a cross-sectional diagram of a manufacturing processaccording to a known example;

FIG. 27 is an explanatory diagram describing the relation between stepform and mask; and

FIG. 28 is an explanatory diagram describing the relation between stepform and mask.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail from the embodimentsshown in the FIGS. 1 through 25.

FIG. 1 shows a cross-sectional diagram of a manufacturing process of thediffraction optical device according to the first embodiment. In Step(1) of FIG. 1, a chromium film 22 is formed on a quartz substrate 21 asa thin film, by means of sputtering to a thickness of 100 nm, andfollowing forming of a resist pattern 23 having a diffraction pattern ofa reference cycle, an etching fluid comprised of a mixture of No. 2cerium ammonium nitrate, perchloric acid, and water is used to removethe chromium film 22 which is not covered with the resist.

In Step (2) of FIG. 1, the quartz substrate 21 is etched to a certaindepth to form a recessed portion 24, by means of the reactive ionetching (RIE) method using a mixed gas of CF₄ and hydrogen. In Step (3)of FIG. 1, the electron beam vapor deposition method is used to form analuminum film 25 serving as a second thin film to fill the recessedportions 24 at a thickness to approximately match the surface of theremaining chromium film 22. Next, in Step (4) of FIG. 1, the resistpattern 23 and the aluminum film 25 thereupon are simultaneously removedby means of the lift-off method. With the process so far, a two-stepstructure of a diffraction pattern at a cycle serving as a reference hasbeen formed, the surface of the quartz substrate has been covered with aneighboring chromium film 22 and an aluminum film 25, and the positionand dimensions of the pattern have been stipulated.

Next, a resist pattern 26 is formed in Step (5) of FIG. 1, and followingremoving of the chromium film 27 not covered by resist by means ofetching fluid, the resist pattern 26 is removed in Step (6) of FIG. 1using the same etching fluid as with Step (1). Further, a resist pattern28 is formed in Step (7) of FIG. 1, and following removing of thecertain aluminum film 29 neighboring the chromium film removed in Step(6) using an etching fluid of a mixture of phosphoric acid, nitric acid,acetic acid, and water, the resist pattern 28 is removed in Step (8) ofFIG. 1.

In Step (9) of FIG. 1, the remaining chromium film 22 and aluminum film24 are used as etching masks, and the quartz substrate 21 is etched to acertain depth with the same RIE method as with Step (2) as aself-alignment method wherein alignment is unnecessary. Finally, in Step(10) of FIG. 1, the chromium film 22 is removed using the same etchingfluid as with Step (1), and the aluminum film is removed using the sameetching fluid as with Step (6). Thus, a diffraction optical devicehaving a high-precision, four-stepped, stair-like structure, withoutgrooves or protrusions owing to alignment errors or pattern dimensionserrors, can be realized.

FIG. 2 shows a cross-sectional diagram of a manufacturing process of thediffraction optical device according to the second embodiment, using thephoto-CVD method. In Step (1) of FIG. 2, a chromium film 32 is formed ona quartz substrate 31 as a first thin film, by means of sputtering to athickness of 100 nm, and following forming of a resist pattern 33 havinga diffraction pattern of a reference cycle, an etching fluid comprisedof a mixture of No. 2 cerium ammonium nitrate, perchloric acid, andwater is used to remove the chromium film 32 which is not covered withthe resist pattern 33.

In Step (2) of FIG. 2, the quartz substrate 31 is etched to a certaindepth to form a recessed portion 34, by means of the RIE method using amixed gas of CF₄ and hydrogen. In Step (3) of FIG. 2, the photo-assistedchemical vapor phase deposition (photo CVD) method, which is performedwhile irradiating the rear side of the quartz substrate 31 (lower sidein the Figure) with light, is used to form an aluminum film 35 servingas a second thin film to fill the recessed portions 34 at a thickness toapproximately match the surface of the remaining chromium film 32, usinga Kr F laser beam 248 nm in wavelength, Al(CH₃)₃, and dinitrogenmonoxide.

With the process so far, a two-step structure of a diffraction patternat a cycle serving as a reference has been formed, the surface of thequartz substrate has been covered with a neighboring chromium film 32and an aluminum film 35, and the position and dimensions of the patternhave been stipulated. Incidentally, the CVD method wherein light is casefrom the rear side is handier than other methods, since hole-filling canbe carried out in a single self-alignment process.

Next, in Step (4) of FIG. 2, a certain resist pattern 36 is formed, andfollowing removing the chromium film 37 on which the resist pattern 36has not been formed is removed in Step (5) of FIG. 2 using the sameetching fluid as with Step (1), the resist pattern 36 is removed.Further, in Step (6) of FIG. 2, a certain resist pattern 38 is formed,and following removing the and the part of the aluminum oxide film 35neighboring the chromium film 32 which is the aluminum oxide film 39 isremoved in Step (5) is removed using a phosphoric acid etching liquid,and then the resist pattern 38 is removed in Step (7) of FIG. 2.

Next, in Step (8) of FIG. 2, the remaining chromium film 32 and aluminumoxide film 35 are used as etching masks, and the quartz substrate 31 isetched to a certain depth with the same RIE method as with Step (2), thechromium film 32 is removed using the same etching fluid as with Step(1), and the aluminum oxide film 35 is removed using the same etchingfluid as with Step (7). Thus, a diffraction optical device having ahigh-precision four-stepped stair-like structure without grooves orprotrusions owing to alignment errors or pattern dimensions errors, canbe realized, as shown in Step (9) of FIG. 2.

The CVD method used here can be carried out with various combinations ofthe quartz substrate 31 transmitting assisting light and various layeredmaterials, such as quartz substrate 31 with titanium oxide, boronnitride, or aluminum. Also, a diffraction optical device having ahigh-precision four-stepped stair-like structure can be realized withthe first chromium thin film in the present embodiment replaced with achromium oxide deposited layer, and the aluminum oxide layer 35 in Step(3) with an aluminum film, using a selective deposition method.

FIG. 3 shows the cross-sectional diagram of a manufacturing process of adiffraction optical device according to a third embodiment, using theCMP or etch-back method. In Step (1) of FIG. 3, a chromium film 42 isformed on a quartz substrate 41 as a first thin film, by means ofsputtering to a thickness of around 100 nm to 200 nm, and followingforming of a resist pattern 43 having a diffraction pattern of areference cycle, a mixed gas of chlorine and oxygen is used with the RIEmethod to remove the chromium film 42 which is not covered with theresist pattern 43. In Step (2) of FIG. 3, the resist pattern 43 isremoved, and then the quartz substrate 41 is etched to a certain depthby means of the RIE method using a gas of a fluorocarbon such as CF₄,CHF₃, or C₄F₈. In Step (3) of FIG. 3, an aluminum film is formed to athickness of around 25 nm to 500 nm as a second thin film by means ofelectron-beam vapor deposition, and the aluminum layer 44 is removed inStep (4) of FIG. 3 until the surface of the remaining chromium film 42is exposed, by means of the DAMASCENE method using the chemicalmechanical polishing (CMP) method, or the etch-back method with etchingfluid.

According to the process so far, the diffraction pattern of a cycleserving as a reference is formed in a two-step structure on the patternsubstrate 41, and the surface of the quartz substrate, and the surfaceof the quartz substrate 41 is covered with a neighboring chromium film42 and aluminum film 44.

Next, in Step (5) of FIG. 3, following forming of the resist pattern 45at the certain position, in Step (6) of FIG. 3 an etching fluidcomprised of a mixture of No. 2 cerium ammonium nitrate, perchloricacid, and water is used to remove the chromium film 46 upon which is notformed the resist pattern 45, following which the resist pattern 45 isremoved. Further, a resist pattern 47 is formed in Step (7) of FIG. 3,the aluminum film 48 neighboring the chromium film 46 removed in Step(6) is removed using the same etching fluid as that used in Step (4),and in Step (8) of FIG. 3, the resist pattern 47 is removed. In Step (9)of FIG. 3, the remaining chromium film and aluminum film 44 are masked,the quartz substrate 41 is etched using the same RIE method as with Step(2), forming a recessed portion 49. In the process so far, thediffraction pattern of a cycle serving as a reference is formed in afour-step structure on the pattern substrate 41.

Next, in Step (10) of FIG. 3, an aluminum layer 50 is formed to athickness of around 25 nm to 500 nm in the same manner as with Step (3),following which the recessed portion 49 formed in Step (9) is filled inStep (11) of FIG. 3 according to the DAMASCENE method. Further, thealuminum film 50 is removed in the same manner as with Step (4). Next, aresist pattern 51 is formed at a certain position in Step (12) of FIG.3, and the chromium film 52 without the resist pattern 51 is removed inStep (13) of FIG. 3 using etching fluid. Further, in Step (14) of FIG.3, a resist pattern 53 is formed, the aluminum films 44 and 50 areremoved in Step (15) of FIG. 3, and the resist pattern 53 is removed inStep (16) of FIG. 3.

Next, in Step (17) of FIG. 3, the remaining chromium film 42 andaluminum films 44 and 50 are masked, and the substrate 41 is etchedaccording to the same RIE method as with Step (2). Finally, in Step (18)of FIG. 3, the remaining chromium film 42 is removed with the sameetching fluid as with Step (1), and the aluminum films 44 and 50 areremoved with the same etching fluid as with Step (4).

Thus, a diffraction optical device having a high-precision eight-steppedstair-like structure without grooves or protrusions owing to alignmenterrors or pattern dimensions errors, can be realized by theself-alignment method. Incidentally, the exposure light L for formingthe patterns in the first through third embodiments is not restricted toultraviolet or far ultraviolet light; rather, electron beams, X-ray, orother exposing techniques can be used.

The substrates 21 and 41 according to the first and third embodimentsare selected appropriately according to the object of use, whether atransmitting type, reflecting type, or mold. However, the material to beetched, i.e., the substrate, and the material comprising the first andsecond thin films must be such which have completely different etchingspeeds and etching conditions in the etching methods to be used, and aratio of selection must be obtainable. Regarding the etching method forthe chromium film and the aluminum film, in addition to the wet etchingmethod and RIE method, dry etching methods such as sputtering etching,ion beam etching, and so forth may be used, as well. Further, thefollowing methods may be used for forming the first and second thinfilms in the first and third embodiments: vacuum vapor deposition,sputtering, ion-beam sputtering, ion plating, CVD, MBE, and so forth.

FIG. 4 is a cross-sectional diagram illustrating a reflectivediffraction optical device according to a fourth embodiment of thepresent invention. As a reflective layer, a chromium layer 62, aluminumlayer 63, and quartz layer 64 are layered by means of electron-beamvapor deposition on a substrate 61 having the multi-stepped structureformed in the first through third embodiments. The chromium layer 62 hasthe function of improving adherence to the substrate 61, the aluminumlayer 63 is a reflective layer, and the quartz layer serves as aprotective film. Silica or quartz or the like are used for the materialof the substrate, and the material and layered structure of thereflective layer is selected such that the functions of each layer canbe fully exhibited according to the wavelengths and environments used.Thus, a diffraction optical device having a high-precision four oreight-stepped stair-like structure without grooves or protrusions owingto alignment errors or pattern dimensions errors, can be realized.

FIG. 5 is a cross-sectional diagram illustrating a diffraction opticaldevice according to a fifth embodiment of the present invention. Asubstrate 65 having the multi-stepped structure formed in the firstthrough third embodiments is used as a mold, and a diffraction opticaldevice is replicated using replicating technique such as the ZP methodor injection method, using photo-setting resin or the like. Thus, adiffraction optical device having a high-precision four or eight-steppedstair-like structure without grooves or protrusions owing to alignmenterrors or pattern dimensions errors, can be realized. Further, it ismore preferable that a reflection preventing film be formed on thediffraction optical device manufactured according to any of: the firstthrough third Embodiments; and the fifth Embodiment.

FIG. 6 is a constructional diagram of a projecting optical system havinga diffraction optical device. In FIG. 6, the diffraction optical device72 according to the present invention is assembled into a common lensgroup 71 of spherical or non-spherical lenses, the surface of the commonlenses 71 having a reflection preventing film formed thereupon.

The diffraction optical device 72 cooperates with the lenses 71 tovarious types of aberration in the optical system, such as coloraberration and Seidel's five aberrations. Such projecting opticalsystems are used in various cameras, replacement lenses forsingle-reflex cameras, office equipment such as photocopiers, projectionexposure devices for manufacturing liquid crystal panels, projectionexposure devices for manufacturing semiconductor chips such as ICs,LCIs, and so forth.

FIG. 7 is a constructional diagram of a projecting optical system, andin FIG. 7, the illumination optical system 73 for providing exposurelight, the mask 74 illuminated by the illumination optical system 73,the projecting optical system 75 for projecting a device pattern imagedrawn in the mask 74, and a glass substrate or silicone substrate 76coated with a resist pattern, are arrayed. The diffraction opticaldevice according to the present invention is assembled into theillumination optical system 73 and projecting optical system 75, and areflection preventing film is formed in the surface of the lensescomprising the illumination optical system 73 and projecting opticalsystem 75.

The exposure light from the illumination optical system 73 is cast ontothe mask 74, and projects the device pattern image drawing on the mask74 onto the glass substrate or silicone substrate 76 by means of theprojecting optical system 75.

FIG. 8 and FIG. 9 show a cross-sectional diagram of the process formanufacturing diffraction optical devices by means of a technique ofexposing the negative resist from the rear, according to the sixthembodiment. First, in Step (1) of FIG. 8, a chromium film 82 is formedon a quartz substrate 81 to a thickness of 100 nm by the sputteringmethod. Further, a reflection preventing layer such as chromium oxide orthe like is formed on the chromium layer to a thickness of 20 to 30 nm,in order to improve patterning resolution. In Step (2) of FIG. 8,photo-resist is applied to this quartz substrate 81, and a first resistpattern 83 is formed with both the line width and space width at 0.35μm. Next, the chromium film 82 is etched with the resist pattern 83 as amask, by means of a parallel plate-type RIE device using chlorine gas ora mixed gas of chlorine gas and oxygen. Next, in Step (3) of FIG. 8, theresist pattern 83 is peeled away by means of the oxygen ashing method orwith a peeling fluid. The pattern of this chrome film 82 defines all ofthe step positions throughout all of the following steps.

In Step (4) of FIG. 8, with the pattern of the chromium film 82 as amask, a parallel plate-type RIE device, for example, using a mixed gasof CF₄ and hydrogen is used to etch the quartz substrate 81 by 61 nm infive minutes, under the conditions of: flow of CF₄ at 20 cm³/min, flowof hydrogen at 3 cm³/min, pressure at 4 Pa, and RF power of 60 W. Next,photo-resist is applied to the substrate 81 and the second resistpattern 84 is formed. The alignment precision at this time needs only tobe half of the line width of the pattern of the chromium film 82, sothis can be achieved with a standard exposing device. This can beapplied to all patterning from the second time on, including otherembodiments, as well.

Next, in Step (5) of FIG. 8, the quartz substrate 81 is etched by 61 nmusing the chromium film 82 pattern and resist pattern 84 as a mask.Following peeling of the resist 84 in Step (6) in FIG. 8, photo-resistis applied again and the third resist pattern 85 is formed. Then, inStep (7) of FIG. 8, the quartz substrate 81 is etched by 61 nm using thechromium film 82 and resist pattern 85 as a mask. Following peeling ofthe resist 85, photo-resist is applied again and the fourth resistpattern 86 is formed.

In Step (8) of FIG. 8, the quartz substrate 81 is etched by 61 nm usingthe resist pattern 86 and the chromium film 82 pattern as a mask. Nextin Step (9) of FIG. 8, applying negative resist and exposing from therear side and developing enables the resist pattern 87 to remain onlywhere there is no chromium pattern, as shown in Step (10) of FIG. 8. Atthis time, the chromium pattern itself serves as the contact mask forexposure of the negative resist, so completely accurate alignment can beperformed.

Next, photo-resist is applied thereupon, and the fifth resist 88 isformed, as shown in Step (11) of FIG. 8. In Step (12) of FIG. 8, theportions of the chromium film not covered with the resist pattern 87 and88 are etched away using an etching fluid comprised of a mixture ofcerium ammonium nitrate, perchloric acid, and water. Further, in Step(13) of FIG. 8, the quartz substrate 81 is etched by 366 nm in 30minutes with the resists 87 and 88 as masks, using the same RIE deviceand etching gas as with Step (3), and under the same conditions as withStep (3). In Step (14) of FIG. 9, following removal of the resistpatterns 87 and 88 by the ashing method, negative-resist is appliedthereto and is exposed from the rear side. Developing this in Step (15)of FIG. 9 enables leaving resist pattern 89 only where there is nochromium pattern.

In Step (16) of FIG. 9, photo-resist is applied thereupon, and the sixthresist 90 is formed. In Step (17) of FIG. 9, the portions of thechromium film not covered with the resist pattern 89 and 90 are etchedaway using the same mixture fluid as with Step (12). Further, in Step(18) of FIG. 9, the quartz substrate 81 is etched by 244 nm in 20minutes with the resists 89 and 90 as masks, using the same RIE deviceand etching gas as with Step (3), and under the same conditions as withStep (3). In Step (19) of FIG. 9, following removal of the resistpatterns 89 and 90 by the ashing method, negative-resist is appliedthereto and is exposed from the rear side and developed in Step (20) ofFIG. 9, which, as shown in Step (21) of FIG. 9, enables leaving resistpattern 91 only where there is no chromium pattern.

Next, photo-resist is applied thereupon, and the seventh resist 92 isformed. In Step (22) of FIG. 9, the portions of the chromium film notcovered with the resist pattern 91 and 92 are etched away using the samemixture fluid as with Step (12). Further, in Step (23) of FIG. 9, thequartz substrate 81 is etched by 122 nm in 10 minutes with the resists91 and 92 as masks, using the same RIE device and etching gas as withStep (3), and under the same conditions as with Step (3). In Step (24)of FIG. 9, the resist patterns 91 and 92 are removed by the ashingmethod. Etching of the pattern of the chromium film 82 is performedusing the same mixture fluid as with Step (12), thereby completing adiffraction optical device having an eight-stepped stair-like structure,or a mold for manufacturing such a diffraction optical device.

The diffraction optical device thus completed with a minimum line widthof 0.35 μm and step offset of 61 nm was measured for diffractionefficiency at a usage wavelength of 248 nm, and the results showed thatthe diffraction efficiency minus loss owing to reflection was 93%, whichis a 2% reduction in diffraction efficiency as compared to the idealvalue. The main cause for this reduction in diffraction efficiency wasdue to margin of error in the line width of the first chromium pattern.

FIG. 10 and FIG. 11 show a cross-sectional diagram of the process formanufacturing diffraction optical devices according to the seventhembodiment. Step (1) through Step (3) in FIG. 10 is the same as Step (1)through Step (3) in FIG. 9 in the sixth embodiment, thereby forming thefirst resist pattern and completing the chromium pattern.

In Step (4) of FIG. 10, photo-resist is applied to the substrate 81 andthe second resist pattern 93 is formed. Next, in Step (5) of FIG. 10,the quartz substrate is etched by 366 nm with the resist pattern 93 andthe chromium film 82 pattern as masks. In Step (6) of FIG. 10, followingpeeling of the resist 93, photo-resist is again applied to the substrate81 and the third resist pattern 94 is formed. Next, in Step (7) of FIG.10, the quartz substrate 81 is etched by 244 nm with the resist pattern94 and the chromium film 82 pattern as masks. Next, following peeling ofthe resist 94, photo-resist is again applied and the fourth resistpattern 95 is formed.

In Step (8) of FIG. 10, the quartz substrate 81 is etched by 122 nm withthe resist pattern 95 and the chromium film 82 pattern as masks. In Step(9) of FIG. 10, following peeling of the resist 95, a polyimide film 96is applied to the entire surface to a thickness of approximately 1 μm bymeans of the spin-coating method. Next, the polyimide film 96 is etchedback by means of oxygen-plasma ashing until the surface of the patternof the chromium film 82 is exposed. In Step (10) of FIG. 10, a resistpattern is applied, forming the fifth resist pattern 97 by means oflithography method. In Step (11) of FIG. 10, the portions of thechromium film not covered with the resist pattern 97 and the polyimidefilm 96 are etched away using an etching fluid comprised of a mixture ofcerium ammonium nitrate, perchloric acid, and water, for example. InStep (12) of FIG. 10, with the resist pattern 97 and the polyimide film96 as a mask, a parallel plate-type RIE device, for example, using amixed gas of CF₄ and hydrogen is used to etch the quartz substrate 81 by366 nm in 30 minutes, under the conditions of: flow of CF₄ at 20cm³/min, flow of hydrogen at 3 cm³/min, pressure at 4 Pa, and RF powerof 60 W.

In Step (13) of FIG. 10, following peeling of the resist pattern 97 andthe polyimide film 96, a polyimide film 98 is applied to the entiresurface to a thickness of approximately 1 μm by means of thespin-coating method. In Step (14) of FIG. 11, the polyimide film 98 isetched back until the surface of the pattern of the chromium film 82 isexposed. Next, in Step (15) of FIG. 11, a resist pattern is applied,forming the sixth resist pattern 99 by means of lithography method. InStep (16) of FIG. 11, the portions of the chromium film not covered withthe resist pattern 99 and the polyimide film 98 are etched away using anetching fluid the same as that used in Step (11).

In Step (17) of FIG. 11, with the resist pattern 99 and the polyimidefilm 98 as a mask, a parallel plate-type RIE device, and etching gas,the same as those used in Step (12), are used to etch the quartzsubstrate 81 by 244 nm in 20 minutes, under the same etching conditions.In Step (18) of FIG. 11, the resist pattern 99 and the polyimide film 98are peeled away. Then, polyimide film 100 is applied to the entiresurface to a thickness of approximately 1 μm by means of thespin-coating method. In Step (20) of FIG. 11, the polyimide film 100 isetched back by means of oxygen-plasma ashing until the surface of thepattern of the chromium film 82 is exposed. Next, in Step (21) of FIG.11, a resist pattern is applied, forming the seventh resist pattern 101by means of lithography method.

In Step (22) of FIG. 11, the portions of the chromium film not coveredwith the resist pattern 101 and the polyimide film 100 are etched awayusing an etching fluid the same as that used in Step (11). In Step (23)of FIG. 11, with the resist pattern 101 and the polyimide film 100 as amask, a parallel plate-type RIE device, and etching gas, the same asthose used in Step (12), are used to etch the quartz substrate 81 by 122nm in 10 minutes, under the same etching conditions. In Step (24) ofFIG. 11, the resist patterns 101 and polyimide film 100 are removed bythe ashing method. Etching of the pattern of the chromium film 82 isperformed using the same mixture fluid as with Step (11), therebycompleting a diffraction optical device having an eight-steppedstair-like structure, or a mold for manufacturing such a diffractionoptical device, as shown in Step (25) of FIG. 11.

FIG. 12 shows a cross-sectional diagram of the process for manufacturingdiffraction optical devices by means of the photo-CVD method, accordingto the eighth embodiment. In Step (1) of FIG. 12, a chromium film 102 isformed on a quartz substrate 81 to a thickness of 100 nm by thesputtering method. Further, a chromium oxide layer is formed on thechromium layer to a thickness of 20 to 30 nm. This chromium oxide layerreduces exposing light reflected by the quartz substrate 81 insubsequent patterning steps, thereby improving patterning resolution. InStep (2) of FIG. 12, photo-resist is applied to this quartz substrate81, and a first resist pattern 104 is formed with both the line widthand space width at 0.35 μm. Next, the chromium film 102 and chromiumoxide film 103 is etched with the resist pattern 104 as a mask, by meansof a parallel plate-type RIE device using chlorine gas or a mixed gas ofchlorine gas and oxygen. Next, the resist 104 is peeled away, completinga chromium oxide/chromium pattern such as shown in Step (3) of FIG. 12.The pattern of this chromium oxide/chromium pattern defines all of thestep positions throughout all of the following steps.

In Step (4) of FIG. 12, with the pattern of the chromium film 102 andchromium oxide film 103 as a mask, a parallel plate-type RIE device, forexample, using a mixed gas of CF₄ and hydrogen is used to etch thequartz substrate 81 by 61 nm in five minutes, under the conditions of:flow of CF₄ at 20 cm³/min, flow of hydrogen at 3 cm³ /min, pressure at 4Pa, and RF power of 60 W. Next, photo-resist is applied to the substrate81 and the second resist pattern 105 is formed. Next, in Step (5) ofFIG. 12, the quartz substrate 81 is etched by 366 nm using the chromiumfilm 102 and chromium oxide film 103 as a mask. Following peeling of theresist 105 in Step (6) in FIG. 12, photo-resist is applied again and thethird resist pattern 106 is formed.

Then, in Step (7) of FIG. 12, the quartz substrate 81 is etched by 244nm using the resist pattern 106, chromium film 102, and chromium oxidefilm 103 as a mask. Following peeling of the resist 106 in Step (8) inFIG. 12, photo-resist is applied again and the fourth resist pattern 106is formed. Then, the quartz substrate 81 is etched by 122 nm using theresist pattern 107, chromium film 102, and chromium oxide film 103 as amask. Next, in Step (9) of FIG. 12, the resist pattern 107 is removed bymeans of the oxygen-plasma ashing method or with a peeling fluid.

In Step (10) of FIG. 12, the substrate in the state of Step (9) isexposed to ultraviolet rays, e.g., a Kr F laser beam, from the rear sidein an Al₂(CH₃)₆ gas. This allows forming of an aluminum film 108 to athickness of 20 to 100 nm, only at the portion where there is nochromium film 102 or chromium oxide film 103. At this time, there isalso precipitation of an aluminum film 109 on the rear side, as well. InStep (11) of FIG. 12, following application of a resist pattern film 110thereupon, the aluminum film 109 on the rear side is removed using amixed fluid of phosphoric acid, nitric acid, acetic acid, and water. InStep (12) of FIG. 12, following removal of the resist pattern 110,photo-resist is applied thereupon and exposed and developed, therebyforming the fifth resist 111.

In Step (13) of FIG. 13, the portions of the chromium film 102 andchromium oxide film 103 not covered with the resist pattern 111 and thealuminum film 108 are removed by etching. Next, in Step (14) of FIG. 13,a parallel plate-type RIE device, and etching gas, the same as thoseused in Step (4), are used to etch the quartz substrate 81 by 366 nm in30 minutes, under the same etching conditions, with the resist pattern111 and aluminum film 108 as a mask.

In Step (15) of FIG. 13, the resist pattern 111 is removed by means ofthe ashing method or with a peeling fluid, and following removing thealuminum film 108 with a mixture fluid the same as that of Step (11),the substrate is exposed to ultraviolet rays, e.g., a Kr F laser beam,from the rear side in an Al₂(CH₃)₆ gas. This allows forming of analuminum film 112 to a thickness of 20 to 100 nm, only at the portionwhere there is no chromium film 102 or chromium oxide film 103. At thistime, there is also precipitation of an aluminum film 113 on the rearside, as well. In Step (16) of FIG. 13, following application of aresist pattern film 114 thereupon, the aluminum film 113 on the rearside is removed using the same mixed fluid as that used in Step (11). InStep (17) of FIG. 13, following removal of the resist pattern 114,photo-resist is applied thereupon and exposed and developed, therebyforming the sixth resist 115.

In Step (18) of FIG. 13, the portions of the chromium film 102 andchromium oxide film 103 not covered with the resist pattern 115 and thealuminum film 112 are removed by etching with an etching fluid comprisedof a mixture of cerium ammonium nitrate, perchloric acid, and water, forexample. Next, in Step (19) of FIG. 13, a parallel plate-type RIEdevice, and etching gas, the same as those used in Step (4), are used toetch the quartz substrate 81 by 224 nm in 20 minutes, under the sameetching conditions, with the resist pattern 115 and aluminum film 112 asa mask. The resist pattern 115 is removed by means of the ashing methodor with a peeling fluid, and the aluminum film 112 is removed by etchingwith a mixed fluid the same as that used in Step (11), resulting in thestate shown in Step (20) of FIG. 13.

This substrate is exposed to ultraviolet rays, e.g., a Kr F laser beam,from the rear side in an Al₂(CH₃)₆ gas. This allows forming of analuminum film 116 to a thickness of 10 to 20 nm, only at the portionwhere there is no chromium film 102 or chromium oxide film 103, as shownin Step (22) of FIG. 13. At this time, there is also precipitation of analuminum film 117 on the rear side, as well. In Step (22) of FIG. 13,following application of a resist pattern film 118 thereupon, thealuminum film 117 on the rear side is removed using the same mixed fluidas that used in Step (11). In Step (23) of FIG. 13, following removal ofthe resist pattern 118, photo-resist is applied thereupon and exposedand developed, thereby forming the seventh resist 119.

In Step (24) of FIG. 13, the portions of the chromium film 102 andchromium oxide film 103 not covered with the resist pattern 119 and thealuminum film 116 are removed by etching with a mixed fluid the same asthat used in Step (18). Next, in Step (25) of FIG. 13, a parallelplate-type RIE device, and etching gas, the same as those used in Step(4), are used to etch the quartz substrate 81 by 122 nm in10 minutes,under the same etching conditions, with the resist pattern 119 andaluminum film 116 as a mask. The resist pattern 119 is removed by meansof the ashing method or with a peeling fluid in Step (26) of FIG. 13,and the aluminum film 116 is removed by etching with a mixed fluid thesame as that used in Step (11). In Step (27) of FIG. 13, the chromiumfilm 102 and chromium oxide film 103 are etched with a mixed fluid thesame as that used in Step (18), thereby completing a diffraction opticaldevice having an eight-stepped stair-like structure, or a mold formanufacturing such a diffraction optical device.

The diffraction optical device thus completed with a minimum line widthof 0.35 μm and step offset of 61 nm was measured for diffractionefficiency at a usage wavelength of 248 nm, and the results showed thatthe diffraction efficiency minus loss owing to reflection was 93%, whichis a 2% reduction in diffraction efficiency as compared to the idealvalue. The main cause for this reduction in diffraction efficiency wasdue to margin of error in the line width of the first chromium pattern,and defective reproduction in etching.

FIG. 14 and FIG. 15 show cross-sectional diagrams of the process formanufacturing diffraction optical devices by means of the DAMASCENEmethod using aluminum, according to the ninth embodiment.

In the same manner as with the sixth embodiment, photo-resist is appliedto the substrate 81 in Step (1) of FIG. 14, a first resist pattern 83 isformed in Step (2) of FIG. 14 by means of photo-lithography, and in Step(3) of FIG. 14, the resist pattern 83 is masked and the chrome film 82is etched.

In Step (4) of FIG. 14, with the pattern of the chromium film 82 as amask, the quartz substrate 81 is etched by 61 nm. Next, photo-resist isapplied to the substrate 81 and the second resist pattern 120 is formedby means of photo-lithography. In Step (5) of FIG. 14, the quartzsubstrate 81 is etched by 366 nm using the resist pattern 120 andchromium film 82 as a mask. Following peeling of the photo-resist 120 inStep (6) in FIG. 14, photo-resist is applied again and the third resistpattern 121 is formed. In Step (7) of FIG. 14, the quartz substrate 81is etched by 244 nm using the resist pattern 121 and chromium film 82pattern as a mask. Next, following peeling of the resist 106,photo-resist is applied again and the fourth resist pattern 122 isformed.

In Step (8) of FIG. 14, the quartz substrate 81 is etched by 122 nmusing the resist pattern 122 and chromium film 82 as a mask. Then, theresist pattern 122 is removed by means of the oxygen-plasma ashingmethod or with a peeling fluid. In step (9) of FIG. 14, an aluminum film123 is formed to a thickness of 1.5 μm by means of the sputteringmethod. Then, polishing the aluminum film 123 with a lapping machineunder the conditions of 30 rpm and 50 g/cm³, using a cerium oxidepolishing agent of a 5/100 μm grain and a urethane sheet polishingcloth, until the surface of the chromium film 82 is exposed, yields thestate such as shown in Step (10) of FIG. 14. In Step (11) of FIG. 13,photo-resist is applied thereupon and exposed and developed, therebyforming the fifth resist 124. In Step (12) of FIG. 14, the portions ofthe chromium film 102 not covered with the resist pattern 124 and thealuminum film 123 are removed by etching with an etching fluid comprisedof a mixture of cerium ammonium nitrate, perchloric acid, and water, forexample.

In Step (13) of FIG. 14, with the resist pattern 124 and aluminum film123 as a mask, a parallel plate-type RIE device, for example, using amixed gas of CF₄ and hydrogen is used to etch the quartz substrate 81 by366 nm in 30 minutes, under the conditions of: flow of CF₄ at 20cm³/min, flow of hydrogen at 3 cm³/min, pressure at 4 Pa, and RF powerof 60 W. After the resist pattern 124 and aluminum film 123 are removedin Step (14) of FIG. 15, an aluminum film 125 is formed to a thicknessof 1.5 μm by means of the sputtering method. Then, polishing thealuminum film 125 with the same lapping machine under the sameconditions as Step (9), until the surface of the chromium film 82 isexposed, yields the state such as shown in Step (15) of FIG. 15. In Step(16) of FIG. 15, photo-resist is applied thereupon and exposed anddeveloped, thereby forming the fifth photo-resist 126.

In Step (17) of FIG. 15, the portions of the chromium film 82 notcovered with the resist pattern 126 and the aluminum film 125 areremoved by etching with the same etching fluid as Step (11). In Step(18) of FIG. 15, with the resist pattern 126 and aluminum film 125 as amask, an RIE device the same as that used in Step S(13) is used to etchthe quartz substrate 81 by 244 nm in 20 minutes, under the same etchingconditions.

Next, the resist pattern 126 is removed by means of the ashing method orwith a peeling fluid, the aluminum film 125 is removed using a mixedfluid of phosphoric acid, nitric acid, acetic acid, and water, yieldingthe state shown in Step (19) of FIG. 15. In Step (20) of FIG. 15, analuminum film 127 is formed to a thickness of 1.5 μm by means of thesputtering method. Then, polishing the aluminum film 127 with the samelapping machine under the same conditions as Step (9), until the surfaceof the chromium film 82 is exposed, yields the state such as shown inStep (21) of FIG. 15. In Step (22) of FIG. 15, photo-resist is appliedthereupon and exposed and developed, thereby forming the sixth resist126.

In Step (23) of FIG. 15, the portions of the chromium film 102 notcovered with the resist pattern 48 and the aluminum film 127 are removedby etching with the same etching fluid as Step (11). Next, in Step (24)of FIG. 15, with the resist pattern 28 and aluminum film 127 as a mask,an RIE device the same as that used in Step (13) is used to etch thequartz substrate 81 by 122 nm in 10 minutes, under the same etchingconditions. Next, the resist pattern 48 is removed by means of theashing method or with a peeling fluid, the aluminum film 127 is removedusing a mixed fluid the same as that used in Step (19), yielding thestate shown in Step (25) of FIG. 15. In Step (26) of FIG. 15, thechromium film 102 is etched with a mixed fluid the same as that used inStep (11), thereby completing a diffraction optical device having aneight-stepped stair-like structure, or a mold for manufacturing such adiffraction optical device.

The diffraction optical device thus completed with a minimum line widthof 0.35 μm and step offset of 61 nm was measured for diffractionefficiency at a usage wavelength of 248 nm, and the results showed thatthe diffraction efficiency minus loss owing to reflection was 93%, whichis a 2% reduction in diffraction efficiency as compared to the idealvalue. The main cause for this reduction in diffraction efficiency wasdue to margin of error in the line width of the first chromium pattern,and defective reproduction in etching.

FIG. 16 shows a cross-sectional drawing of a reflective steppeddiffraction optical device according to a tenth embodiment. Thereflective stepped diffraction optical device such as shown in FIG. 16is completed by using the sputtering method to form a 100 nm aluminumfilm on: a stair-like substrate such as shown in FIG. 8 and FIG. 9manufactured according to the sixth embodiment, a stair-like substratesuch as shown in FIG. 10 and FIG. 11 manufactured according to theseventh embodiment, a stair-like substrate such as shown in FIG. 12 andFIG. 13 manufactured according to the eighth embodiment, or a stair-likesubstrate such as shown in FIG. 14 and FIG. 15 manufactured according tothe ninth embodiment.

The diffraction optical device thus completed with a minimum line widthof 0.35 μm and step offset of 61 nm was measured for diffractionefficiency at a usage wavelength of 248 nm, and the results showed thatthe diffraction efficiency minus loss owing to reflection was 91%, whichis a 4% reduction in diffraction efficiency as compared to the idealvalue. The main cause for this 4% reduction in diffraction efficiencywas due to margin of error in the line width of the first chromiumpattern, defective reproduction in etching, and the shape of the steppedportion becoming less clear-cut due to the sputtering.

FIGS. 17 through 19 show cross-sectional diagrams of the manufacturingprocessed of the diffraction optical device according to the eleventhembodiment. The steps (1) through (24) in FIG. 17 and FIG. 18 areexactly the same as the steps (1) through (24) in FIG. 8 and FIG. 9according to the first embodiment, except for the etching depth andetching time, so only the differing points shall be listed, and detaileddescription shall be omitted.

In step (3) of FIG. 17, with the pattern of the chromium film 82 as amask, the quartz substrate 81 is etched by 30.5 μm for 2.5 minutes.

In step (13) of FIG. 17, with the resist patterns 87 and 88 as a mask,the quartz substrate 81 is etched by 183 μm for 15 minutes.

In step (18) of FIG. 18, with the resist patterns 89 and 90 as a mask,the quartz substrate 81 is etched by 122 μm for10 minutes.

In step (24) of FIG. 18, with the resist patterns 91 and 92 as a mask,the quartz substrate 81 is etched by 61 μm for 5 minutes.

Using the technique wherein negative resist is exposed from the rearunder the above conditions, a substrate 81 such as shown in step (24) inFIG. 18 is formed. Incidentally, the technique need not be rearexposure, but rather may be the DAMASCENE method using aluminum, theetch-back method, or the photo-CVD method using rear irradiation.

In step (25) of FIG. 19, an aluminum film 130 is formed to a thicknessof 1.5 μm by means of the sputtering method. Then, polishing thealuminum film 123 according to the DAMASCENE method with a lappingmachine under the conditions of 30 rpm and 50 g/cm³, using a ceriumoxide polishing agent of a 5/100 μm grain and a urethane sheet polishingcloth, until the surface of the chromium film 82 is exposed, yields thestate such as shown in Step (26) of FIG. 19. Incidentally, the techniqueneed not be the DAMASCENE method using aluminum, but rather may be rearexposure of negative resist, the etch-back method, or the photo-CVDmethod using rear irradiation. In Step (27) of FIG. 19, photo-resist isapplied thereupon and exposed and developed, thereby forming the seventhresist pattern 131.

In Step (28) of FIG. 19, the portions of the chromium film 82 notcovered with the resist pattern 131 and the aluminum film 130 areremoved by etching with an etching fluid comprised of a mixture ofcerium ammonium nitrate, perchloric acid, and water, for example. InStep (29) of FIG. 19, photo-resist is applied thereupon and exposed anddeveloped, thereby forming the eighth resist pattern 132. Next, thealuminum film 130 not covered by the resist pattern 132 in this state isremoved using a mixed fluid of phosphoric acid, nitric acid, aceticacid, and water, yielding the state shown in Step (30) of FIG. 19.

In Step (31) of FIG. 19, the photo-resist 132 is removed by means of theoxygen-plasma ashing method or with a peeling fluid. In Step (31) ofFIG. 19, with the chromium film 82 and aluminum film 130 as a mask, aparallel plate-type RIE device, for example, using a mixed gas of CF₄and hydrogen is used to etch the quartz substrate 81 by 244 nm in 20minutes, under the conditions of: flow of CF₄ at 20 cm³/min, flow ofhydrogen at 3 cm³/min, pressure at 4 Pa, and RF power of 60 W. Next,etching the aluminum film 130 with the same mixed fluid as that used instep (30) to remove it yields the state such as shown in Step (33) ofFIG. 19. Next, the chromium film 82 is etched with a mixed fluid thesame as that used in Step (30), thereby completing a diffraction opticaldevice having a 16-stepped stair-like structure.

The diffraction optical device thus completed with a minimum line widthof 0.35 μm and step offset of 30.5 nm was measured for diffractionefficiency at a usage wavelength of 248 nm, and the results showed thatthe diffraction efficiency minus loss owing to reflection was 97%, whichis a 2% reduction in diffraction efficiency as compared to the idealvalue. The main cause for this reduction in diffraction efficiency wasdue to margin of error in the line width of the first chromium pattern,and incorrect etching depth.

FIG. 20 and FIG. 21 show cross-sectional diagrams of the process formanufacturing diffraction optical devices, according to the twelfthembodiment. In Step (1) of FIG. 20, a chromium film 102 is formed on aquartz substrate 81 to a thickness of 100 nm by the sputtering method,to form the state shown in step (2) of FIG. 20. Photo-resist is appliedto this quartz substrate 81, and a first resist pattern is formedthereupon with both the line width and space width at 0.35 μm, by meansof photo-lithography. Next, the chromium film 82 is etched with theresist pattern as a mask, by means of a parallel plate-type RIE deviceusing chlorine gas or a mixed gas of chlorine gas and oxygen. Next, thephoto-resist is peeled away, completing a chromium pattern such as shownin Step (3) of FIG. 20. The chromium pattern defines all of the steppositions throughout all of the following steps.

In Step (4) of FIG. 20, with the pattern of the chromium film 82 as amask, a parallel plate-type RIE device, for example, using a mixed gasof CF₄ and hydrogen is used to etch the quartz substrate 81 by 61 nm infive minutes, under the conditions of: flow of CF₄ at 20 cm³/min, flowof hydrogen at 3 cm³/min, pressure at 4 Pa, and RF power of 60 W. Next,in Step (5) of FIG. 20, photo-resist is applied to the substrate 81 andthe second resist pattern 133 is formed. In Step (6) of FIG. 20, thequartz substrate 81 is etched by 122 nm using the resist pattern 133 andchromium film 82 pattern as a mask. Peeling of the resist 133 yields astate such as shown in Step (7) in FIG. 20.

In step (8) of FIG. 20, an aluminum film 134 is formed to a thickness of1.5 μm by means of the sputtering method. Then, polishing the aluminumfilm 134 with a lapping machine under the conditions of 30 rpm and 50g/cm³, using a cerium oxide polishing agent of a 5/100 μm grain and aurethane sheet polishing cloth, until the surface of the chromium film82 is exposed, yields the state such as shown in Step (9) of FIG. 20. InStep (10) of FIG. 20, photo-resist is applied thereupon and exposed anddeveloped, thereby forming the fifth resist 135. In Step (11) of FIG.20, the portions of the chromium 16 not covered with the resist pattern135 and the aluminum film 134 are removed by etching with an etchingfluid comprised of a mixture of cerium ammonium nitrate, perchloricacid, and water, for example.

Next, in Step (12) of FIG. 20, with the resist pattern 135 and aluminumfilm 134 as a mask, an RIE device the same as that used in Step (4) isused to etch the quartz substrate 81 by 122 nm in 10 minutes, under thesame etching conditions. Next, the resist pattern 135 is removed-bymeans of the ashing method or with a peeling fluid, and the aluminumfilm 134 is removed using a mixed fluid of phosphoric acid, nitric acid,acetic acid, and water, yielding the state shown in Step (13) of FIG.20.

The substrate in the sate of step (13) in FIG. 20 is exposed toultraviolet rays, e.g., a Kr F laser beam, from the rear side in anAl₂(CH₃)₆ gas. This allows forming of an aluminum oxide film 136 to athickness of 500 nm, only at the portion where there is no chromium film82, and at this time, there is also precipitation of an aluminum film136 on the rear side, as well. In the event that the aluminum oxide film136 on the rear side is unnecessary, this can be removed by applying aresist film thereupon, and removing with phosphoric acid as shown inStep (14) of FIG. 20. In Step (15) of FIG. 21, photo-resist is appliedthereupon and exposed and developed, thereby forming the fifth resist138.

In step (17) of FIG. 21, the portion of the aluminum oxide film 136 notcovered with the resist pattern 138 is removed with phosphoric acid. Instep (18) of FIG. 21, the resist pattern 138 is removed by means of theashing method or with a peeling fluid, and photo-resist 139 is appliedin step (19) of FIG. 21. Next, in step (20) of FIG. 21, a resist pattern140 is formed by the photo-lithography method. In step (21) of FIG. 21,the portion of the chromium film 82 not covered with the resist pattern140 is removed with the same mixed fluid as that used in step (11).Next, the resist pattern 140 is removed, yielding the state shown instep (22) of FIG. 21.

In Step (23) of FIG. 21, with the chrome film 82 and aluminum oxide film136 as a mask, an RIE device the same as that used in Step (4) and amixed gas of CF₄ and hydrogen are used to etch the quartz substrate 81by 244 nm in 20 minutes, under the same etching conditions. In step (24)of FIG. 21, the portion of the aluminum oxide film 136 is removed byetching with phosphoric acid. Finally, the chromium film 82 is removedby etching using a mixed fluid the same as that used in step (11) forexample, and an aluminum film 49 is formed on the stair-shaped substrateto a thickness of 100 nm, thus completing a reflection-type steppeddiffraction optical device such as shown in step (25) of FIG. 21.

The diffraction optical device thus completed with a minimum line widthof 0.35 μm and step offset of 61 nm was measured for diffractionefficiency at a usage wavelength of 248 nm, and the results showed thatthe diffraction efficiency minus loss owing to reflection was 91%, whichis a 4% reduction in diffraction efficiency as compared to the idealvalue. The main cause for this reduction in diffraction efficiency wasdue to margin of error in the line width of the first chromium pattern,and defective etching reproducibility. Incidentally, the diffractionefficiency of an example formed according to the known method was 76%,clearly demonstrating the advantages of the present invention.

FIG. 22 shows a cross-sectional drawing of the manufacturing process ofa stepped diffraction optical device formed of resin, according to athirteenth embodiment. The stair-like substrate such as shown in FIG. 8and FIG. 9 manufactured according to the sixth embodiment, thestair-like substrate such as shown in FIG. 10 and FIG. 11 manufacturedaccording to the seventh embodiment, the stair-like substrate such asshown in FIG. 12 and FIG. 13 manufactured according to the eighthembodiment, or the stair-like substrate such as shown in FIG. 14 andFIG. 15 manufactured according to the ninth embodiment, is used as amold.

First, in step (11) of FIG. 22, response-hardening resin 152, i.e.,ultraviolet photo-setting resin or heat-setting resin such as acrylicsor epoxies is dropped on the glass substrate 151 from a syringe 150.Next, as shown in step (2) of FIG. 22 and step (3) of FIG. 22, thestepped substrate mold 153 is pressed from above the resin 152, thusforming a replica-layer 154. A separating agent is applied to thesurface of the stair-shaped portion before pressing the steppedsubstrate mold 153 into the resin 152, as necessary.

Next, in the event that the resin is ultraviolet photo-setting resin,ultraviolet light is irradiated from the side of the stepped substratemold 153, hardening the resin. In the event that the resin isheat-setting resin, heat is applied to harden the resin. Then, removingthe stepped substrate mold 153 completes a stepped diffraction opticaldevice 155 such as shown in step (4) of FIG. 22.

The diffraction optical device thus completed with a minimum line widthof 0.35 μm and step offset of 120 nm was measured for diffractionefficiency at a usage wavelength of 500 nm, and the results showed thatthe diffraction efficiency was 90%, which is a 5% reduction indiffraction efficiency as compared to the ideal value. The main causefor this reduction in diffraction efficiency was due to margin of errorin the line width of the first chromium pattern, defective etchingreproducibility, and shrinkage and the like of the resin 147.

FIG. 23 shows a constructional diagram of a stepper which is a exposuredevice for semiconductor use, according to a fourteenth embodiment.Arrayed in order from above are a 248 nm wavelength illumination opticalsystem 160, a reticle 161, imaging optical system 162, and a state 163on which is mounted a semiconductor substrate W, with the diffractionoptical device D manufactured according to the method of the firstembodiment assembled therein, in order to reduce color aberration withinthe imaging optical system 162 and to provide non-spherical effects.

With this stepper, ultraviolet rays such as Kr F or i rays areirradiated from the illumination optical system 160 to the reticle 161,and the pattern drawn on the reticle 161 is drawn on the semiconductorplate on the stage 163 at ⅕ reduction magnification, by means of theimaging optical system 162.

FIG. 24 is a perspective view of the diffraction optical device D, andFIG. 25 is a cross-sectional view of the cross-sectional state thereof.This diffraction optical device D has the same optical functions as aconvex lens, representing a 4-step diffraction optical device with stepoffset of 61 nm, width of one step on the outermost perimeter of 0.35μm, and 120 mm in diameter.

The light cast into the diffraction optical device D is mainly dividedinto first order, ninth order, and seventeenth order diffracted lightand is transmitted through the device D. Of these, only the light of thefirst order has effects on the imaging, and consists of 93% of theincident light. The remaining several percent are the ninth order andseventeenth order light, but these are of diffraction orders far removedfrom the first order light necessary for imaging, so these head outwardsfrom the imaging optical system, and do not affect the imaging much.

Accordingly, in the event of using an 8-step diffraction optical deviceaccording to the known method wherein three masks 17 a, 17 b, and 17 care used in manufacturing under the same conditions (step offset of 61nm, width of one step on the outermost perimeter of 0.35 μm, and 120 mmin diameter) as shown in FIG. 27, third order diffraction light isstrongly generated between the first order and ninth order diffractionlight, so the unwanted light forms pseudo-patterning on the image andthe resolution deteriorates, but this problem can be avoided by means ofusing the 8-step diffraction optical device according to the presentinvention under the same conditions.

What is claimed is:
 1. A lithographic method for manufacturing adiffraction optical device having multi-stepped, stair-like structuresformed on a substrate, wherein each structure has at least threestair-like steps, said method comprising the steps of: a first stepcomprising forming a first masking pattern comprising a first maskingmaterial in a pattern of lines, spaces and recessed portions on saidsubstrate, wherein the recessed portions are in the spaces of said firstmasking pattern; a second step of forming a second masking patterncomprising a second masking material in a pattern of lines and spaces onsaid substrate by filling the recessed portions formed on said substrateby said first step with said second masking material, wherein the spacesof said second masking pattern correspond to the lines of the firstmasking pattern; a third step comprising forming a third masking patternby etching a portion of the lines of said first and second maskingmaterials; and a fourth step comprising etching said substrate throughsaid third masking pattern, said third masking pattern comprisingnon-etched portions of said first and second masking patterns.
 2. Amethod according to claim 1, wherein in said second step, said secondmasking material is deposited using a forming method selected from thegroup consisting of: the etch-back method, the lift-off method, theDAMASCENE method, and the selective deposition method.
 3. A methodaccording to claim 1, wherein in said second step, said substrate iscomprised of translucent material, said first masking material is alight-shielding material, and said second masking material is depositedby means of a photo-assisted deposition method in which light is castfrom the rear side of the substrate.
 4. A method according to any of theclaims 1 through 3, wherein said first and second masking materials areselected from the group consisting of: metals, oxides, and nitrides. 5.A method for manufacturing a mold for manufacturing diffraction opticaldevices, said method comprising the steps of: providing a base materialthat is partially covered with a first mask having diffraction patterncycle portions; etching portions of the base material not covered withsaid first mask; then covering portions of said first mask other thanthe diffraction pattern cycle portions, with a second mask; repeatingthe above steps at least once; then covering the portions of the basematerial not covered with said first mask with a third mask; coveringportions of said first mask other than the diffraction pattern cycleportions with said third mask and a fourth mask; removing the portionsof said first mask that are not masked with said third and fourth masks;then etching said base material; and repeating the above steps at leastonce.
 6. A method for manufacturing diffraction optical devices, saidmethod comprising the steps of: providing a base material that ispartially covered with a first mask having diffraction pattern cycleportions; etching portions of the base material not covered with saidfirst mask; then covering portions of said first mask other than thediffraction pattern cycle portions with a second mask; repeating theabove steps at least once; then covering the portions of the basematerial not covered with said first mask with a third mask; coveringportions of said first mask other than the diffraction pattern cycleportions with said third mask and a fourth mask; removing the portionsof said first mask that are not masked with said third and fourth masks;then etching said base material; and repeating the above steps at leastonce.
 7. A method for manufacturing diffraction optical devicesaccording to claim 6, wherein said first mask is formed oflight-shielding material, said base material is comprised of translucentmaterial, said third mask is formed of negative resist, wherein saidnegative resist is photosensitized by light transmitted through saidbase material from the rear side of said base material, and wherein theportions of the base material not covered with said first mask arecovered with negative resist which is said third mask.
 8. A method formanufacturing diffraction optical devices according to claim 6, saidmethod comprising the steps of: etching portions of said base materialnot covered with a first mask; then covering portions of said first maskother than the diffraction pattern cycle portions with a second mask;repeating the step of etching the base material of the portions notcovered with a mask at least once; forming a thin film over the entiresurface with a material serving as a third mask which is comprised of amaterial different from the material of said first mask and said basematerial; etching said third mask until the surface of said first maskis exposed; and covering the portions of the base material not coveredwith said first mask with said third mask.
 9. A method for manufacturingdiffraction optical devices according to claim 6, said method comprisingthe steps of: etching portions of said base material not covered with afirst mask; then covering portions of said first mask other than thediffractive pattern cycle portions with a second mask; repeating thestep of etching the base material of the portions not covered with amask at least once; forming a thin film over the entire surface with amaterial serving as a third mask which is comprised of a materialdifferent from the material of said first mask and said base material;polishing said third mask until the surface of said first mask isexposed; and then covering the portions of the base material not coveredwith said first mask with said third mask.
 10. A method formanufacturing diffraction optical devices according to claim 6, whereinsaid first mask is formed of light-shielding material, said basematerial is comprised of translucent material, wherein the portions ofthe base material not covered with said first mask are covered with saidsecond mask by means of exposing the surface being worked at the time ofmanufacturing said third mask with a gas containing a desired material,and causing reaction with said gas by means of light being transmittedthrough said base material from the rear side of said base material. 11.A method for manufacturing diffraction optical devices according to anyof the claims 6, through 10, wherein said first mask is formed of achromium film.
 12. A method for manufacturing diffraction opticaldevices according to any of the claims 6, through 10, wherein said firstmask is a two-layer structure of light-reflecting material andreflection-preventing material, with the light-reflecting material beingprovided proximate to said base material.
 13. A method for manufacturingdiffraction optical devices according to any of the claims 6, through10, wherein said first mask is a two-layer structure of chromium filmand chromium oxide film, with the chromium film being provided proximateto said base material.
 14. A method for manufacturing diffractionoptical devices according to any of the claims 6, through 10, wherein alight-reflecting film is provided on the etched surface in the finalstep of said manufacturing steps.
 15. A method for manufacturingdiffraction optical devices, said method comprising the steps of:providing a base material that is partially covered with a first maskhaving diffraction pattern cycle portions; etching portions of the basematerial not covered with said first mask; then covering portions ofsaid first mask other than the diffraction pattern cycle portions with asecond mask; etching portions of the base material not covered with amask; repeating the above steps at least once; then covering theportions of the base material not covered with said first mask with athird mask; covering portions of said first mask other than thediffraction pattern cycle portions with said third mask and a fourthmask; removing the portions of said first mask that are not masked; thenrepeating at least once a step of etching said base material; removingsaid third mask and fourth mask; covering the portions of the basematerial not covered with said first mask with a fifth mask; thencovering every other portion of said first mask with a sixth mask;removing the portions of said first mask that are not covered by saidfifth and sixth mask; then covering every other portion of said fifthmask with a seventh mask; removing the portions of said fifth mask thatare not covered by said seventh mask; etching said base material at theportions not covered by said fifth mask and said first mask; and finallyremoving the remaining said fifth mask and said first mask.
 16. A methodfor manufacturing diffraction optical devices according to claim 15,wherein said first mask is formed of light-shielding material, said basematerial is comprised of translucent material, said third mask is formedof negative resist, wherein said negative resist is photosensitized bylight transmitted through said base material from the rear side of thebase material, and wherein the portions of the base material not coveredwith said first mask are covered with negative resist which is saidthird mask.
 17. A method for manufacturing diffraction optical devicesaccording to claim 15, said method comprising the steps of: etchingportions of said base material not covered with a first mask; thencovering portions of said first mask other than the diffraction patterncycle portions with a second mask repeating the step of etching the basematerial of the portions not covered with a first mask at least once;forming a thin film over the entire surface with a material serving as athird mask which is comprised of a material different to the material ofsaid first mask and said base material; etching said third mask untilthe surface of said first mask is exposed; and covering the portions ofthe base material not covered with said first mask with said third mask.18. A method for manufacturing diffraction optical devices according toclaim 15, said method comprising the steps of: etching portions of saidbase material not covered with a first mask; then covering portions ofsaid first mask other than the diffractive pattern cycle portions with asecond mask; repeating the step of etching the base material of theportions not covered with a first mask at least once; forming a thinfilm over the entire surface with a material serving as a third maskwhich is comprised of a material different to the material of said firstmask and said base material; polishing said third mask until the surfaceof said first mask is exposed; and then covering the portions of thebase material not covered with said first mask with said third mask. 19.A method for manufacturing diffraction optical devices according toclaim 15, wherein said first mask is formed of light-shielding material,said base material is comprised of translucent material, whereinportions of the base material not covered with said first mask arecovered with said second mask by means of exposing the surface of thebase material and first mask to a gas, and causing reaction with saidgas by means of light being transmitted through said base material fromthe rear side of said base material.
 20. A method for manufacturingdiffraction optical devices according to any of the claims 15 through19, wherein said first mask is formed of light-shielding material, saidbase material is comprised of translucent material, said fifth mask isformed of negative resist, wherein said negative resist isphotosensitized by light transmitted through said base material from therear side of said base material, and wherein portions of the basematerial not covered with said first mask are covered with negativeresist which is said fifth mask.
 21. A method for manufacturingdiffraction optical devices according to any of the claims 15 through19, said method comprising the steps of: etching portions of said basematerial not covered with said first mask; then covering portions ofsaid first mask other than the diffractive pattern cycle portions with asecond mask; repeating the step of etching the base material of theportions not covered with the first mask at least once; then coveringthe portions of the base material not covered with said first mask witha third mask; covering portions of said first mask other than thediffractive pattern cycle portions with said third mask and said fourthmask; removing the portions of said first mask that are not masked; thenrepeating at least once a step of etching said base material; thenremoving said third mask and fourth mask; forming a thin film over theentire surface with a material serving as a fifth mask which iscomprised of a material different to the material of said first mask andsaid base material; etching said fifth mask until the surface of saidfirst mask is exposed; and covering the portions of the base materialnot covered with said first mask with said fifth mask.
 22. A method formanufacturing diffraction optical devices according to any of the claims15 through 19, said method comprising the steps of: etching portions ofsaid base material not covered with said first mask; then coveringportions of said first mask other than the diffraction pattern cycleportions with a second mask; repeating the step of etching the basematerial of the portions not covered with the first mask at least once;then covering between said first mask with a third mask; coveringportions of said first mask other than the diffraction pattern cycleportions with said third mask and said fourth mask; removing theportions of said first mask that are not masked; then repeating at leastonce of etching said base material; then removing said third mask andfourth mask; forming a thin film over the entire surface with a materialserving as a fifth mask which is comprised of a material different tothe material of said first mask and said base material; polishing saidfifth mask until the surface of said first mask is exposed; and coveringthe portions of the base material not covered with said first mask withsaid fifth mask.
 23. A method for manufacturing diffraction opticaldevices according to any of the claims 15 through 19, wherein said firstmask is formed of light-shielding material, said base material iscomprised of translucent material, wherein the portion of the basematerial not covered with said first mask is covered with said secondmask by means of exposing the surface being worked at the time ofmanufacturing said fifth mask with a gas containing a desired material,and causing reaction with said gas by means of light being transmittedthrough said base material from the rear side of said base material. 24.A method for manufacturing diffraction optical devices according to anyof the claims 15 through 19, wherein said first mask is formed of achromium film.
 25. A method for manufacturing diffraction opticaldevices according to any of the claims 15 through 19, wherein said firstmask is a two-layer structure of light-reflecting material andreflection-preventing material, with the light-reflecting material beingprovided proximate to said base material.
 26. A method for manufacturingdiffraction optical devices according to any of the claims 15 through19, wherein said first mask is a two-layer structure of chromium filmand chromium oxide film, with the chromium film being provided proximateto said base material.
 27. A method for manufacturing diffractionoptical devices according to any of the claims 15 through 19, wherein alight-reflecting film is provided on the etched surface in the finalstep of said manufacturing steps.
 28. A lithographic method for formingan element having multi-stepped, stair-like structures on a substrate,wherein each structure has three or more stair-like steps, comprising: astep comprising alternately forming first and second masks withdiffering materials; a step comprising etching portions of said firstand second masks to form a third mask; and a step comprising etching thesubstrate through said third mask, said third mask comprising non-etchedportions of said first and second masks.
 29. A method for forming threeor more steps on a substrate, said method comprising the steps of:forming a first mask on an area of said substrate corresponding withevery other step, and performing at least one of etching or depositionon an area of said substrate on which said first mask is not formed; andforming a second mask on an area of said substrate on which said firstmask has not been formed, and performing at least one of etching ordeposition on the area of said substrate on which neither of said firstand said second masks is formed.
 30. A forming method according to claim29, wherein said number of steps is 2n (n being a natural number of from2 to 8).
 31. A forming method according to claim 29, wherein said firstmask is formed of metal.
 32. A forming method according to claim 31,wherein said second mask is formed of metal or photo-resist.
 33. Aforming method according to claim 32, wherein said plurality of stepsact as diffraction grating.
 34. A forming method according to claim 33,wherein said plurality of steps have differing dimensions.
 35. A formingmethod according to claim 31, wherein a plurality of said steps areformed on said substrate.
 36. A lithographic method of manufacturing anelement having multi-stepped, stair-like structures on a substrate,wherein each structure has at least three stair-like steps, comprising:(a) defining a position of a first stair-like step in said eachstair-like structure by a masking pattern of lines formed on thesubstrate; and (b) defining the position of each subsequent stair-likestep by a portion of the lines of the masking pattern formed in saidstep (a) and another masking pattern.